The main challenge was to create a practical time display on the 8x8 LED matrix. The outer LEDs are used to show the minutes (to the nearest 5) and I designed a 4x4 pixel "font" to show the hour on the inner LEDs. Here's the time display in demo (sped up) mode:http://www.youtube.com/watch?v=niVspPjHHfI

The unit has additional display modes: the time in words, the temperature, a "Matrix" style animation and random pseudo-words (taken from my Loquino project http://www.flickr.com/photos/funnypolynomial/sets/72157629076673753/). The display mode is selected by changing the orientation of the unit, determined by an accelerometer. From the standard position (displaying the time as above) tipping the unit over to the left shows the Matrix animation, to the right shows the temperature. Turning it upside down shows the time in words.http://www.youtube.com/watch?v=1O97MwmAgRw

The unit has no buttons. The time is set by changing the orientation. For example tipping the unit face up, rotating it anti-clockwise and then lying it flat puts it into hour setting mode. The hour automatically increments. The current hour is set by rotating the unit back to the standard position. Repeating the process sets the minutes.http://www.youtube.com/watch?v=rj8n6pWyV-0

The unit includes a light sensor to dim the LEDs when the ambient light dips below a threshold. The alternate brightness and ambient threshold are set as above, but with a clockwise rotation.

I also spent a fair bit of time creating a semi-cryptic wordless instruction sheet. Just diagrams and icons, drawn using PostScript code in an isometric projection:Matrix Clock - Instructions by funnypolynomial, on Flickr